Process of treating metal



apolis, Ind, assignors to -Belt Company,

ChicagoJlL, a corporation of Illinois No Drawing. Application April 22,1932,

v Serial No. 606,907

This invention relates to the process of treating metal and particularlyto a process which involves the treatment of a body of metal to formupon it or introduce within its mass another element which combines andalloys with the metal of the original mass. I

It has for one object, therefore, to form upon at mass of metal a layerof an alloy in which the metal of the original mass and the addedelement are alloyed together.

It has for another object to introduce into the body of the originalmetal, to a greater or a less depth, another element which alloys withthe original metal so that the original metal is alloyed throughout apart of-or all of its mass.

' The. process involves the step of carrying one element into a mass ofmetal to become alloyed with it. 7 It has been found that the halogengases, such as bromine, chlorine, iodine and fluorine, will act ascarriers for certain elements by com;-

. bining at high temperatures with them to form gaseous compounds ofthem and when such a gaseous compound of an element and a halogen gas isbrought intocontact wlth,a body of metal at suitable temperatures andfor suitable' times, the gaseous compound will be carried into themetallic body and will produce an alloy in which the metal combines withthe element which was introduced in the gaseous form.

I One example of this process involves the use of chromium and chlorinewith a ferrous metal to form an iron-chrome alloy in the ferrous metal.

At sumciently high temperatures chromium comblues with chlorine to forma chromium-chloride gas, which may be chrpmicor chromus-chloride. Ingeneral in the specification and in the claims, where we use-theexpression "chromic-chloride or chromous-chloride we mean any gaseouscombination of chromium and chlorine. Iron-or steel when subjected tothis chromicor chrom- .ous-chloride gas will take up the chromium and aniron-chromium alloy is formed, first at the surface of the mass of ironand upon continued subjection of the iron to the chromicorchromouschloride gas, the chromium penetrates increasingly into the ironand thus the depth of the layer of alloy is increased. If the process iscontinued suficiently, the entire mass of metal is alloyed with thechromium.

In practice, for the sake of economy, it is usually advisable to use themost common and the most cheaply produced of the halogens; this ischlorine and it is readily produced from common. salt. One practicalapplication of our process involves the following steps: Iron castingsare packed in ferro-chromium and salt and are then heated forapproximately three hours at a temperature of 1700 F.-l900 F. Uponcooling it is found that the castings have absorbed some of the chromiumto form a layer of high chromium alloy.

Hard iron castings may be packed, as above described, and put throughthe normal annealing treatment which in usual practice, without thespecial packing, would malleableize them and it is found that after theusual annealing cycle, due 1 to the ferro-chromium and salt packing, theresulting castings have a chromium, alloy surface layer, and the usualsoft malleable core. Thus the malleableizing of the hard iron castingshas been effected during the same process in which the chromium alloylayer is produced. In either case, whether the process includes themaileableizing step or not, it is believed that the chromium wastransferred to the iron by the ,not in contact with the chromium, haveshown u that the chromium is can'ied over by the gas an alloyed with theiron by this method.

For certain p rposes and particularly forthe sake of greater cheapness,other chrouim bearing materials may be used in the pacmng. Thus chromiteore, which is the raw source of chromium, may be used in a packing ofsalt, sand and pulverized coal or charcoal. This puking, in addition tofurnishing the chromium necessary, is arranged to take care of theoxygen which is present in the chromite ore. The examples abovementioned refer specifically only to the use of chromium, but theinvention is not limited to the use of that element alone and theparticular steps inthe method, the temperature and materials involved,arementioned only as illustrating one application of the method. Manyothers may be made. u

Frequently it is desirable to carry out the alloying as a part of anannealing or malleableizing treatment. A typical example of this isgiven below, in which the steps for making a chromium alloy during anannealing cycle are discussed. It will be understood that alloys of anyof the elements or of several of them in combination may similarly becarried out during an annealing operation. a

If hard iron castings are submitted to the usual malleableizing cycle ortreatment, in the presence of a packing including ferro-chromium or someother source of chromium and salt or some other source of a halogen gas,the usual malleableizing effect will be accomplished and at the sametime and during the same process the chromiz- 'ing will take place andas before, in the simple carbon out of combination with the iron. Whilethis will not take place completely, the major part of the. iron carbideis thus removed. The casting is then cooled to a point somewhat aboveits'critical temperature in the neighborhood of 1350 F., and during thiscooling a further quantity of the carbon is thrown out of combination.In the usual method the carbon that still remains in combination'isthrown out by controlling the final cooling, so that it occursvery,slow= ly through the critical temperature range, the

as HOW-F. to 1900" Fito cause the formation of.

the chromic-' or-chromous-chloride gas andto' permit its penetrationi'n'to' the iron'to the desired cooling'being as slow at 5 F. per hourand the final cooling alone frequently requiring 48 hours. Where themalleableizing is thus carried out and the formation of the chromiumalloy is to occur at the same time, the packing above indicated is used,in addition to the usual packing for malleableizing, and the temperaturemust be as high "degree; Many modifications of this malleableizing'cycle are used and" generally in most ofthem the'step oF-aHoyIng may beincluded, provided only that the proper'fingredintsam introduced to"produce the gaseous-compound of chromium "and a halogen and-tha't theproper temperatures 40 areattained forits production.

E 1; The method of coating and "alloying 'chrowith a ferrousmetal' ofthe group'consistingbf'iron and steelwhi'ch includes the steps ofplacing the ferrous metal together with 'common salt and a source ofchromiumselected from the group of materials consisting of metallic andsodium-andcause-direot combination of the Y mu; metal with saidchromium.

chromium, chromite ore and ferrochromium in acontainer, heating saidcontainer andcontents to a point sufficient to break down the salt tochlorine and sodium and cause direct combination of the chlorine andchromium, and free the 5 sodium for action as a reducing agent on theferrous metal, and alloying and coating the surface of the ferrous metalwith said chromium.

2. The method of coating and alloying chromium with a ferrous metal ofthe group consisting it of iron and steel which includes the steps ofplac-. ing the ferrous metal together with common salt. andferro-chromium in a container heatmg said container and contents to apoint suflicient to break down the'salt to chlorine and sodium and 15cause direct combination of the chlorine and chromium, and free thesodium for action as a reducing agent on the ferrous metal, and alloyingand coating the surface of the ferrous metal" with said chromium.

3. The method of coating and alloying chromium with a ferrous metal ofthe group consisting of iron and steel which includes the steps ofplacing the ferrous metal together with common salt and metallicchromium in a container, heat- 2% ing said container and contents to apoint sufficient to break down the salt to chlorine and sodium and causedirect combination of the.chlo-.' rine and chromium, and free the sodiumfor action as a reducing agent on the ferrous metal, and 39 alloyingandcoating the surface of the'ferrous metalwith said chromium. I i

4'. The method of coating and alloying chromiwith a ferrous metal of thegroup consisting of iron and steel which includes the steps of mac- 35ing the ferrous metal together with common salt and chromite ore and areducingagent in a container, heating said container and contents to apoint ;suiilcient to breakdown the'salt to chlorine chlorine andchromium,l'and free the'sodium for action as a reducing agent onthe'ferrous-metal, and'auomng and coating' the surface-oi thefer- PAULF.

